<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        input{
            width: 300px;
            height: 30px;
            display: block;
            border: none;
            outline: none;
            margin: 15px;
            border: 1px solid #dee0e9;
            padding: 0 15px;
            border-radius: 15px;
        }
        /* 定制
        -webkit Chrome 浏览器的内核 Safari 内核也是
        input-placeholder scrollbar 实验中的属性 前面加-webkit
        */
        .placeholder-custom::-webkit-input-placeholder{
            color: #babbc1;
            font-size: 12px;
        }
    </style>
</head>
<body>
    <input type="text" class="placeholder-custom" placeholder="请输入用户名搜索">
    <input type="text" placeholder="请输入用户名搜索">
</body>
</html>